Use more specific selector for finding options of a select

I'm using Select2 with Ember.js. Ember automatically inserts `script` tags for its own purposes, which breaks Select2's placeholder. The generated html looks like this:

```html
<select>
  <script id="metamorph-7-start" type="text/x-placeholder"></script>
  <option value=""></option>
  <script id="metamorph-7-end" type="text/x-placeholder"></script>
</select>
```

With this small PR, Select2 works with Ember seamlessly.